The present invention is directed to reflection and projection displays and more particularly to micro-electromechanical shutter assemblies for use in such displays.
Techniques for fabricating micro-electromechanical devices have been set forth in various articles in technical journals. Additionally, patents have issued which address light modulation through the use of micro-electromechanically devised shutters. In particular, U.S. Pat. No. 5,078,479 to Vuilleumier describes a light modulation device with matrix addressing. Each cell of the matrix has two flaps fixed to a substrate by flexible attachments, by proper application of electrical charges, the flaps are activated to twist to a position allowing passage or blockage of light.
A patent to Worley, U.S. Pat. No. 5,552,925 describes a micro-electromechanical shutter array using micro-electromechanical technology and silicon-on-transparent-substrate technology. The array is operated using electro-static forces which allow for the twisting of the shutter which is set forth as a rotor.
A laser beam modulator is described in a paper by Obermeier et al. (Univ. Berlin). A rectangular 2-segment shutter suspended from torsion rods is used to demonstrate the concept of large angle deflection of a torsionally suspended shutter under the influence of an electrostatic force between the plates of a 90.degree.-angle capacitor. The scale of the described shutters are lmm with 450 .mu.m long torsion rods. The shutters are used in an analog mode, i.e. there's no address electrode, only a bias voltage. The shutters and hinges are shown as being made of polysilicon, Al and Cr/Au.
Obermeier et al. reports lifetimes in the order of 10.sup.5 cycles for the materials they have used (Poly, Al or Cr/Au). For these materials, the springs need to be designed in a way the stress at 90.degree. is below the fatigue limit or elastic stress limit. These materials are likely to require longer, thinner torsion rods than single crystal silicon.
Texas Instruments is known to be working on DMD projection display technology, i.e. using a DC bias voltage to achieve bi-stability and passive matrix addressability with low voltage switching only. Differences between this work and the present invention include the large angle mode, the geometry of the devices, the application to which the devices are applied (direct view vs. projection) and the scale (TI pixels are 17 .mu.m or so).
Other micro-electromechanical shutter devices are disclosed, for example in U.S. Pat. No. 5,226,099 to Mignardi et al.; U.S. Pat. No. 5,459,602 to Sampsell; U.S. Pat. No. 4,383,255 to Grandjean, et al.; U.S. Pat. No. 4,564,836 to Vuilleumier, et al.; U.S. Pat. No. 4,584,056 to Perret et al.; and U.S. Pat. No. 5,579,149 to Moret et al.